Its not arguable. Hamas is in possession of the Gaza strip, just because its not recognized by other nations does not make it less true. Hezzbolah is in control of parts of southern Lebanon, just because the Lebanese government can't or won't do anything about it doesn't make it less true. Are you saying Russia does not control Crimea just because Europe and the US wish they didn't? They have the guns, they have the infrastructure in those regions, they control them.

India has been a much more reasonable government for its history, Pakistan has fought multiple wars with India, and both countries have had strained relations with China at times, the need for a deterrent is obvious. But even still, we did try to ensure both countries did not get nuclear weapons, even though they were much, much more reasonable countries. India and Pakistan argue over who should control Kashmir, and though each country has radicals, the governments of those nations have never argued that the entire populations of their enemy should be wiped out. Iran, their leaders, have argued for this. Before '79 Israel enjoyed great relations with Iran, because it made sense, both nations had poor relations with the Arab nations of the region. But the Islamic government in Iran has an ideological reason to hate Israel, its not a question of power politics, its a fundamental belief that Israel should not exist, and that slaughter is an acceptable means to remove them.

But EVEN STILL, one of the greatest dangers of Iran getting nuclear weapons, has little to do with Israel, even if it further endangers them (and others). If Iran gets nuclear weapons, the other Arab states of the region, who are not Iran's friends, have a strong incentive to get them as well. I don't particularly fear what Jordan's King would do with them, nor the military government of Egypt, nor Saudi Arabia's current King. Although it would be just as dangerous as two rational nations like the US and the USSR having them, bad things can happen that neither side wanted, leading to a result neither side wanted. But Jordan, Saudi Arabia and Egypt all have very radical, very murderous Islamists in their society. None of those countries are as stable as say the US, Russia, China, Britain, France, Israel or India. Those weapons could fall into murderous hands, and could result in a tragedy far worse than the world has seen in a long time. Not to mention, Iran has those same murderous elements in its society, even if it is somewhat stable.

Its not black and white, very few international conflicts are, that doesn't mean that one side isn't much more in the right than the other, it doesn't mean we don't have very good reasons to choose sides.